Assessment of the hepatic circulation in humans: new concepts based on evidence derived from a D-sorbitol clearance method

A high value of serum des-γ-carboxy prothrombin before hepatocellular carcinoma treatment can be associated with long-term liver dysfunction after treatment

BACKGROUND

Transcatheter arterial chemoembolization (TACE) is an effective treatment for hepatocellular carcinoma (HCC), but it sometimes makes liver function worse. The pre-TACE prediction of liver dysfunction after TACE would be helpful to avoid long-term liver dysfunction.

METHODS

We performed a case-control study in 100 HCC patients who underwent TACE at Kobe University Hospital. Urinary/blood biochemical examinations were performed before TACE. As an indicator of liver function, Child's score was also evaluated before and 3 months after TACE. Cases with and without an increase of 2 points or more in the Child's score were compared, and independent risk factors were statistically examined. A pre-TACE predictive model of an increase of 2 points or more in the Child's score after TACE was developed using logistic regression.

RESULTS

Univariate analyses showed that des-γ-carboxy prothrombin (DCP) and lactate dehydrogenase (LDH) before TACE were significantly higher in the Child's score-deteriorated group than in the group with no deterioration (p = 0.036 and 0.003, respectively). All possible multivariate regressions showed that DCP (p = 0.003) and LDH (p = 0.002) were independent factors determining the deterioration of Child's class. A predictive model was developed, as follows: exp(0.014 × LDH + 0.572 × ln(DCP) - 8.655)/(1 + exp(0.014 × LDH + 0.572 × ln(DCP) - 8.655)). The model discriminated well, with AUC being 0.837 (95 % confidence interval [CI] 0.662-1.000). The optimal cut-off point was 0.073, and the sensitivity and specificity were 90.9 and 69.7 %, respectively.

CONCLUSIONS

High values of DCP and LDH before TACE were associated with the long-term deterioration of liver function. Our pre-therapeutic prediction model could be useful to identify high-risk cases.

Lidocaine/monoethylglycinexylidide test, galactose elimination test, and sorbitol elimination test for metabolic assessment of liver cell bioreactors

Various metabolic tests were compared for the performance characterization of a liver cell bioreactor as a routine function assessment of cultures in a standby for patient application in clinical studies. Everyday quality assessment (QA) is essential to ensure a continuous level of cellular functional capacity in the development of hepatic progenitor cell expansion systems providing cells for regenerative medicine research; it is also of interest to meet safety requirements in bioartificial extracorporeal liver support systems under clinical evaluation. Quality criteria for the description of bioreactor cultures were developed using primary porcine liver cells as a model. Porcine liver cells isolated by collagenase perfusion with an average of 3 x 10(9) primary cells were used in 39 bioreactors for culture periods up to 33 days. Measurements of monoethylglycinexylidide synthesis and elimination of lidocaine, galactose elimination, and sorbitol elimination proved to be useful for routine QA of primary liver cell cultures. We demonstrate two methods for dispensing test substances, bolus administration and continuous, steady-state administration. Bolus test data were grouped in Standard, Therapy, Infection/Contamination, and Cell-free control groups. Statistical analyses show significant differences among all groups for every test substance. Post hoc comparisons indicated significant differences between Standard and Cell-free groups for all elimination parameters. For continuous tests, results were categorized according to number of culture days and time-dependent changes were analyzed. Continuous administration enables a better view of culture health and the time dependency of cellular function, whereas bolus administration is more flexible. Both procedures can be used to define cell function. Assessment of cellular function and bioreactor quality can contribute significantly to the quality of experimental or clinical studies in the field of hepatic bioreactor development.

Noninvasive functional liver blood flow measurement: comparison between bolus dose and steady-state clearance of sorbitol in a small-rodent model

Plasma clearance of D-sorbitol, a nontoxic polyol, occurs predominantly in the liver and has been used to measure functional liver blood flow after bolus and steady- state intravenous administration. However, it is not known which of these two administration methods is superior. Therefore, plasma D-sorbitol clearance was studied in an animal model both after a bolus dose and under steady-state (SS) conditions and compared directly with liver blood flow, under normal conditions, and after the induction of endotoxin (LPS) sepsis. Adult male Wistar rats (526 +/- 38 g body wt; n = 27) were anesthetized and mechanically ventilated. Hemodynamics, hepatic arterial flow, and portal venous flow were measured. Two groups were studied, namely healthy animals that served as controls and a sepsis group that received 5 mg/kg LPS intravenously (Escherichia coli O127:B8). Each animal received either a SS infusion (0.1 mg/100 g body wt per min) or a bolus (3 mg/100 g body wt) of a 5% D-sorbitol solution intravenously in a randomized order. After the initial measurements and a 60-min pause time in between (T(1/2,sorbitol) = 9 min), a crossover was done. The hepatic clearance of D-sorbitol in the control group showed a good correlation between bolus and SS (Spearman's r = 0.7681, P = 0.0004), and both techniques correlated well with total liver blood flow (TLBF) (r = 0.7239, P = 0.0023 and r = 0.7226, P = 0.0023, respectively). Also in the sepsis group there was a good correlation between bolus and SS sorbitol clearance (r = 0.6655, P = 0.0182). In the sepsis group, only the SS clearance correlated with TLBF (r = 0.6434, P = 0.024). In conclusion, in normal and under septic conditions, hepatic clearance of D-sorbitol either by bolus or a SS infusion is comparable. In healthy animals, this also correlated well with TLBF but not in septic conditions. However, this is expected because of the changes in the liver microcirculation, shunting, and decreased hepatocyte function in sepsis.

Assessment of the hepatic microvascular changes in liver cirrhosis by perfusion computed tomography

AIM: To assess the hepatic microvascular parameters in patients with liver cirrhosis by perfusion computed tomography (CT).

METHODS: Perfusion CT was performed in 29 patients without liver disease (control subjects) and 39 patients with liver cirrhosis, including 22 patients with compensated cirrhosis and 17 patients with decompensated cirrhosis, proved by clinical and laboratory parameters. CT cine-scans were obtained over 50 s beginning with the injection of 50 mL of contrast agent. Hepatic microvascular parameters, mean transit time (MTT) and permeability surface area product (PS) were obtained with the Perfusion 3 software (General Electric, ADW 4.2).

RESULTS: The overall differences of MTT and PS between control subjects, patients with compensated cirrhosis and those with decompensated cirrhosis were statistically significant (P = 0.010 and P = 0.002, respectively). MTT values were 15.613 ± 4.1746 s, 12.592 ± 4.7518 s, and 11.721 ± 4.5681 s for the three groups, respectively, while PS were 18.945 ± 7.2347 mL/min per 100 mL, 22.767 ± 8.3936 mL/min per 100 mL, and 28.735 ± 13.0654 mL/min per 100 mL. MTT in decompensated cirrhotic patients were significantly decreased compared to controls (P = 0.017), whereas PS values were remarkably increased (P = 0.001).

CONCLUSION: The hepatic microvascular changes in patients with liver cirrhosis can be quantitatively assessed by perfusion CT. Hepatic microvascular parameters (MTT and PS), as measured by perfusion CT, were significantly altered in decompensated cirrhosis.

Pharmacokinetics and dosage adjustment in patients with hepatic dysfunction

The liver plays a central role in the pharmacokinetics of the majority of drugs. Liver dysfunction may not only reduce the blood/plasma clearance of drugs eliminated by hepatic metabolism or biliary excretion, it can also affect plasma protein binding, which in turn could influence the processes of distribution and elimination. Portal-systemic shunting, which is common in advanced liver cirrhosis, may substantially decrease the presystemic elimination (i.e., first-pass effect) of high extraction drugs following their oral administration, thus leading to a significant increase in the extent of absorption. Chronic liver diseases are associated with variable and non-uniform reductions in drug-metabolizing activities. For example, the activity of the various CYP450 enzymes seems to be differentially affected in patients with cirrhosis. Glucuronidation is often considered to be affected to a lesser extent than CYP450-mediated reactions in mild to moderate cirrhosis but can also be substantially impaired in patients with advanced cirrhosis. Patients with advanced cirrhosis often have impaired renal function and dose adjustment may, therefore, also be necessary for drugs eliminated by renal exctretion. In addition, patients with liver cirrhosis are more sensitive to the central adverse effects of opioid analgesics and the renal adverse effects of NSAIDs. In contrast, a decreased therapeutic effect has been noted in cirrhotic patients with beta-adrenoceptor antagonists and certain diuretics. Unfortunately, there is no simple endogenous marker to predict hepatic function with respect to the elimination capacity of specific drugs. Several quantitative liver tests that measure the elimination of marker substrates such as galactose, sorbitol, antipyrine, caffeine, erythromycin, and midazolam, have been developed and evaluated, but no single test has gained widespread clinical use to adjust dosage regimens for drugs in patients with hepatic dysfunction. The semi-quantitative Child-Pugh score is frequently used to assess the severity of liver function impairment, but only offers the clinician rough guidance for dosage adjustment because it lacks the sensitivity to quantitate the specific ability of the liver to metabolize individual drugs. The recommendations of the Food and Drug Administration (FDA) and the European Medicines Evaluation Agency (EMEA) to study the effect of liver disease on the pharmacokinetics of drugs under development is clearly aimed at generating, if possible, specific dosage recommendations for patients with hepatic dysfunction. However, the limitations of the Child-Pugh score are acknowledged, and further research is needed to develop more sensitive liver function tests to guide drug dosage adjustment in patients with hepatic dysfunction.

Pharmacokinetics and dosage adjustment in patients with hepatic dysfunction

The liver plays a central role in the pharmacokinetics of the majority of drugs. Liver dysfunction may not only reduce the blood/plasma clearance of drugs eliminated by hepatic metabolism or biliary excretion, it can also affect plasma protein binding, which in turn could influence the processes of distribution and elimination. Portal-systemic shunting, which is common in advanced liver cirrhosis, may substantially decrease the presystemic elimination (i.e., first-pass effect) of high extraction drugs following their oral administration, thus leading to a significant increase in the extent of absorption. Chronic liver diseases are associated with variable and non-uniform reductions in drug-metabolizing activities. For example, the activity of the various CYP450 enzymes seems to be differentially affected in patients with cirrhosis. Glucuronidation is often considered to be affected to a lesser extent than CYP450-mediated reactions in mild to moderate cirrhosis but can also be substantially impaired in patients with advanced cirrhosis. Patients with advanced cirrhosis often have impaired renal function and dose adjustment may, therefore, also be necessary for drugs eliminated by renal exctretion. In addition, patients with liver cirrhosis are more sensitive to the central adverse effects of opioid analgesics and the renal adverse effects of NSAIDs. In contrast, a decreased therapeutic effect has been noted in cirrhotic patients with beta-adrenoceptor antagonists and certain diuretics. Unfortunately, there is no simple endogenous marker to predict hepatic function with respect to the elimination capacity of specific drugs. Several quantitative liver tests that measure the elimination of marker substrates such as galactose, sorbitol, antipyrine, caffeine, erythromycin, and midazolam, have been developed and evaluated, but no single test has gained widespread clinical use to adjust dosage regimens for drugs in patients with hepatic dysfunction. The semi-quantitative Child-Pugh score is frequently used to assess the severity of liver function impairment, but only offers the clinician rough guidance for dosage adjustment because it lacks the sensitivity to quantitate the specific ability of the liver to metabolize individual drugs. The recommendations of the Food and Drug Administration (FDA) and the European Medicines Evaluation Agency (EMEA) to study the effect of liver disease on the pharmacokinetics of drugs under development is clearly aimed at generating, if possible, specific dosage recommendations for patients with hepatic dysfunction. However, the limitations of the Child-Pugh score are acknowledged, and further research is needed to develop more sensitive liver function tests to guide drug dosage adjustment in patients with hepatic dysfunction.

Aging muscle

Age causes structural and functional changes in skeletal muscle in a wide range of species, including humans. Muscle changes in humans start in the fourth decade of life and cause frailty and disabilities. Associated changes in body composition form the basis of many metabolic disorders, such as insulin resistance, type 2 diabetes, hypertension, and hyperlipidemia, which result in an increased incidence of cardiovascular death. Decreases in the synthesis rates of many muscle proteins, specifically of myosin heavy chain and mitochondrial proteins, occur with age. The underlying causes of the reduction in mitochondrial biogenesis and ATP production seem to be decreases in mitochondrial DNA and messenger RNA. Reduced ATP production could be the basis of reduced muscle protein turnover, which requires energy. Both aerobic exercise and resistance exercise enhance muscle protein synthesis and mitochondrial biogenesis. Insulin and amino acids have also been shown to enhance muscle mitochondrial biogenesis and mitochondrial protein synthesis. However, the insulin-induced increase in muscle mitochondrial ATP production is defective in type 2 diabetic patients with insulin resistance. Moreover, a dissociation between increases in muscle mitochondrial biogenesis and insulin sensitivity after exercise has been noted in older persons. It remains to be determined whether muscle mitochondrial dysfunction causes or results from insulin resistance. Exercise seems to enhance the efficiency of muscle mitochondrial DNA in rodents. Reduced physical activity as a contributor of age-related mitochondrial dysfunction remains to be determined. It is proposed that a reduction in tissue mitochondrial ATP production signals the hypothalamic centers to reduce spontaneous physical activities. Voluntary physical activity is regulated by cognitive centers and could attenuate the progressive decline in mitochondrial functions that occurs with age.

The Hepatic Sinusoid in Aging and Cirrhosis

The fenestrated sinusoidal endothelium ('liver sieve') and space of Disse in the healthy liver do not impede the transfer of most substrates, including drugs and oxygen, from the sinusoidal lumen to the hepatocyte. Plasma components transfer freely in both directions through the endothelial fenestrations and into the space of Disse. The endothelium is attenuated, there is no basement membrane and there is minimum collagen in the space of Disse, thus minimising any barriers to substrate diffusion. Both cirrhosis and aging are associated with marked structural changes in the sinusoidal endothelium and space of Disse that are likely to influence bulk plasma transfer into the space of Disse, and diffusion through the endothelium and space of Disse. These changes, termed capillarisation and pseudocapillarisation in cirrhosis and aging, respectively, impede the transfer of various substrates. Capillarisation is associated with exclusion of albumin, protein-bound drugs and macromolecules from the space of Disse, and the progressive transformation of flow-limited to barrier-limited distribution of some substrates. There is evidence that the sinusoidal changes in cirrhosis and aging contribute to hepatocyte hypoxia, thus providing a mechanism for the apparent differential reduction of oxygen-dependent phase I metabolic pathways in these conditions. Structural change and subsequent dysfunction of the liver sieve warrant consideration as a significant factor in the impairment of overall substrate handling and hepatic drug metabolism in cirrhosis and aging.

Functional hepatic flow in patients with liver cirrhosis

AIM: To evaluate hepatic reserve function by investigating the change of functional hepatic flow and total hepatic flow in cirrhotic patients with portal hypertension.

METHODS: HPLC method was employed for the determination of concentration of D-sorbitol in human plasma and urine. The functional hepatic flow (FHF) and total hepatic flow (THF) were determined by means of modified hepatic clearance of D-sorbitol combined with duplex doppler color sonography in 20 patients with cirrhosis and 10 healthy volunteers.

RESULTS: FHF, evaluated by means of the D-sorbitol clearance, was significantly reduced in patients with cirrhosis in comparison to controls (764.74 ± 167.91 vs 1 195.04 ± 242.97 mL/min, P < 0.01). While THF was significantly increased in patients with cirrhosis in comparison to controls (1 605.23 ± 279.99 vs 1 256.12 ± 198.34 mL/min, P < 0.01). Portal blood flow and hepatic artery flow all were increased in cirrhosis compared to controls (P < 0.05 and P < 0.01). D-sorbitol total clearance was significantly reduced in cirrhosis compared to control (P < 0.01), while D-sorbitol renal clearance was significantly increased in cirrhosis (P < 0.05). In controls FHF was similar to THF (1 195.05 ± 242.97 vs 1 256.12 ± 198.34 mL/min, P = 0.636), while FHF was significantly reduced compared with THF in cirrhosis (764.74 ± 167.91 vs 1 605.23 ± 279.99 mL/min, P < 0.01).

CONCLUSION: Our method that combined modified hepatic clearance of D-sorbitol with duplex doppler color sonography is effective in the measurement of FHF and THF. FHF can be used to estimate hepatic reserve function.

Evaluation of liver functional reserve by combining D-sorbitol clearance rate and CT measured liver volume

AIM: Our research attempted to evaluate the overall functional reserve of cirrhotic liver by combination of hepatic functional blood flow, liver volume, and Child-Pugh’s classification, and to discuss its value of clinical application.

METHODS: Ninety two patients with portal hypertension due to hepatic cirrhosis were investigated. All had a history of haematemesis and hematochezia, esophageal and gastric fundus varices, splenomegaly and hypersplenia. A 2-year follow-up was routinely performed and no one was lost. Twenty two healthy volunteers were used as control group. Blood and urine samples were collected 4 times before and after intravenous D-sorbitol infusion. The hepatic clearance (CL_H) of D-sorbitol was then calculated according to enzymatic spectrophotometric method while the total blood flow (Q_TOTAL) and intrahepatic shunt (R_INS) were detected by multicolor Doppler ultrasound, and the liver volume was measured by spiral CT. Data were estimated by t-test, variance calculation and chi-squared test. The relationships between all these parameters and different groups were investigated according to Child-Pugh classification and postoperative complications respectively.

RESULTS: Steady blood concentration was achieved 120 mins after D-sorbitol intravenous infusion, which was (0.358 ± 0.064) mmol·L^-1 in cirrhotic group and (0.189 ± 0.05) mmol·L^-1 in control group (P < 0.01). CL_H = (812.7 ± 112.4) mL·min^-1, Q_TOTAL = (1280.6 ± 131.4) mL·min^-1, and R_INS = (36.54 ± 10.65)% in cirrhotic group and CL_H = (1248.3 ± 210.5) mL·min^-1, Q_TOTAL = (1362.4 ± 126.9) mL·min^-1, and R_INS = (8.37 ± 3.32)% in control group (P < 0.01). The liver volume of cirrhotic group was 1057 ± 249 cm³, 851 ± 148 cm³ and 663 ± 77 cm³ in Child A, B and C group respectively with significant difference (P < 0.001). The average volume of cirrhotic liver in Child B, C group was significantly reduced in comparison with that in control group (P < 0.001). The patient, whose liver volume decreased by 40% with the CL_H below 600 mL·min^-1, would have a higher incidence of postoperative complications. There was no strict correspondent relationship between CL_H, liver volume and Child-Pugh’s classification.

CONCLUSION: The hepatic clearance of D-sorbitol, CT measured liver volume can be reliably used for the evaluation of hepatic functional blood flow and liver metabolic volume. Combined with the Child-Pugh’s classification, it could be very useful for further understanding the liver functional reserve, therefore help determine reasonable therapeutic plan, choose surgical procedures and operating time.

Capillarization of the sinusoids in liver fibrosis: noninvasive assessment with contrast-enhanced MRI in the rabbit

Sinusoidal capillarization induces microcirculatory changes in liver cirrhosis and fibrosis. The purpose of this study was to assess whether contrast-enhanced MRI can be used to demonstrate the effects of sinusoidal capillarization in liver fibrosis. Dynamic MRI after injection of a low-molecular-weight contrast agent of 0.56 kDa (Gd-DOTA), and two high-molecular-weight contrast agents of 6.47 kDa and 52 kDa (P792 and P717) was performed in rabbits with liver fibrosis induced by cholesterol and diethylstilbestrol. The hepatic distribution volume accessible to the high-molecular-weight agents decreased in the rabbits with liver fibrosis (P792: 7.8% +/- 1.7% vs. 10.1% +/- 1.8% in normal rabbits, P =.038; P717: 6.2% +/- 2.1% vs. 9.7% +/- 1.6% in normal rabbits, P =.007), whereas the hepatic mean transit time (MTT) of the low-molecular-weight agent was increased (15.9 +/- 8.0 s vs. 8.8 +/- 2.6 s in normal rabbits, P =.015). In rabbits with liver fibrosis, the clearance of indocyanine green (ICG) was correlated with the volume accessible to the high-molecular-weight agents (P792: r = 0.810, P =.015; P717: r = 0.857, P =.007). The collagen content of the liver was inversely correlated with the distribution volume of P717 (r = -.833, P =.010) and with the ICG clearance (r = -.810, P =.015). It was concluded that the microcirculatory changes induced by sinusoidal capillarization in liver fibrosis can be demonstrated noninvasively with MRI.

Correlation between midazolam and lignocaine pharmacokinetics and MEGX formation in healthy volunteers

AIMS

The objectives of the present investigation were: (a) to determine the correlation between lignocaine and midazolam pharmacokinetics following intravenous administration in healthy volunteers, (b) to determine the effects of treatment with an inhibitor of CYP3A4 (erythromycin) on this correlation and (c) to assess the precision of the MEGX-test as a sole predictor of lignocaine and midazolam pharmacokinetics.

METHODS

The study was conducted in four male and four female healthy volunteers, aged between 21 and 26 years, who received 1 mg kg-1 lignocaine HCl i.v. on days 1, 3, 5, 9 and 10 of the investigation. On days 5 and 10 they also received midazolam, 0.075 mg kg-1 i.v. and from days 6-10 they took erythromycin 500 mg orally, four times daily. Following administration of lignocaine and midazolam, frequent venous blood samples were obtained for determination of the concentrations of lignocaine, MEGX and midazolam.

RESULTS

In the absence of erythromycin a statistically significant linear correlation was observed between the clearance of lignocaine and midazolam (CL(midazolam)= 0.41 x CL(lignocaine)+ 1.2; r(2) = 0.857; P < 0.001). Erythromycin cotreatment resulted in a loss of the correlation between the two clearances (r(2) = 0.39; P = 0.1). Erythromycin caused a statistically significant reduction in midazolam clearance from the original value of 3.8 to 2.5 (95% CI for the difference -2.27, -0.35) ml kg-1 min-1. Interestingly there was no significant change in the clearance of lignocaine (6.4 vs 5.8 (95% CI for the difference -2.74, -1.51) ml kg-1 min-1). Furthermore no correlation at all was observed between the MEGX-test and lignocaine or midazolam clearances. Considering the data on day 1, 3 and 5 the intra-individual coefficient of variation in the MEGX-test was 45.3% at 15 min and 23.5% at 30 min, respectively.

CONCLUSIONS

It is concluded that there is a significant correlation between lignocaine and midazolam clearances but this correlation is lost after CYP3A4 inhibition by erythromycin. The MEGX-test is of no value in assessing intra- and inter-individual variability in midazolam clearance.

Laboratory assessment of hepatic hemodynamics

Although the study of hepatic circulation is complicated by the dual blood supply and complex anatomy of the liver, many distinct methods are available to facilitate its study. Before embarking on an investigation of hepatic hemodynamics, the investigator must be familiar with the available methods and their applications. All methods have their own attributes and limitations. No one method is superior to the others, but, depending on the aspect of hepatic hemodynamics to be investigated, a particular methodology may yield distinct advantages.

Hepatic perfusion parameters in chronic liver disease: dynamic CT measurements correlated with disease severity

OBJECTIVE

The aim of our study was to determine if hepatic perfusion parameters measured with CT change in relation to disease severity in patients with chronic liver disease.

SUBJECTS AND METHODS

Dynamic contrast-enhanced single-section CT scans of the liver were obtained in 40 individuals who included six control subjects, 16 patients with noncirrhotic chronic liver disease, and 18 patients with cirrhosis. Hepatic, aortic, and portal venous time-density curves were fitted to a dual-input one-compartment model to calculate the liver perfusion, arterial fraction, distribution volume, and mean transit time.

RESULTS

Liver perfusion decreased in patients with cirrhosis (67 +/- 23 mL. min(-1). 100 mL(-1) versus 108 +/- 34 mL. min(-1). 100 mL(-1) in control subjects [p = 0.009] and 98 +/- 36 mL. min(-1). 100 mL(-1) in patients with noncirrhotic chronic liver disease [p = 0.003]), and the arterial fraction and the mean transit time increased (41 +/- 27% and 51 +/- 79 sec versus 17 +/- 16% and 16 +/- 5 sec in control subjects, and 19 +/- 6% and 17 +/- 8 sec in patients with noncirrhotic chronic liver disease [p < 0.05]). A significant correlation was seen between these three perfusion parameters and the severity of chronic liver disease based on clinical and biologic data (p < 0.001). No significant change in distribution volume was observed.

CONCLUSION

Hepatic perfusion parameters measured with CT were significantly altered in cirrhosis and correlated with the severity of chronic liver disease.

Sorbitol as a marker for drug-induced decreases of variable duration in liver blood flow in healthy volunteers

OBJECTIVE

Sorbitol has been suggested as a suitable marker to assess liver blood flow (LBF), after it was shown to adequately reflect prolonged changes in LBF but changes of a shorter duration have not been investigated. We therefore used sorbitol to evaluate drug-induced decreases in LBF of variable duration with i.v. infusions of somatostatin and its synthetic analogue octreotide.

METHODS

In a double-blind, placebo controlled, randomised study, six healthy males received sorbitol for 170 min. At sorbitol steady state, which was at 45 min after the start of the infusion (t=0), somatostatin or octreotide was infused for 30 min. Sampling for sorbitol assay and echo-Doppler hepatic portal vein flow measurements were done regularly and treatments were compared using ANOVA.

RESULTS

The sorbitol AUC over the 30-min intervention period was 15% (95% C.I.: +4, +22%) and 13% (+5, +24%) higher compared to placebo after somatostatin and octreotide respectively. The decline of sorbitol levels after termination of the intervention was faster for somatostatin compared to octreotide, demonstrated by the difference in the AUC (0-2 h) with placebo which was 8% (-3, +19%) lower after somatostatin, and 15% (+5, +26%) after octreotide. Portal venous blood flow decreased during the 30-min interventions; after somatostatin 27% (-14, -40%) and after octreotide 29% (-17, -42%). Portal flow was lower than placebo during the entire experiment after octreotide 30% (-10, -50%), but not after somatostatin 13% (-33, +7%). Changes in sorbitol levels and portal venous blood flow occurred simultaneously and were well correlated for each individual, making it likely that the interventions did not interfere with metabolism.

CONCLUSION

Sorbitol can be used to adequately assess decreases in LBF of variable duration in healthy volunteers.

Interpretation of simultaneous measurements of hepatic extraction fractions of indocyanine green and sorbitol: evidence of hepatic shunts and capillarization?

Sorbitol and indocyanine green (ICG) have high hepatic extraction fractions (E(sorb) and E(ICG)) in normal subjects. A curved relationship has been observed between E(sorb) and E(ICG) in liver disease. According to one interpretation, the decrease of E(sorb) is a result of intrahepatic shunting and 1 - E(sorb) is the fraction of shunted flow (the shunt hypothesis). Under the further assumption that capillarization of functioning sinusoids prevents hepatic uptake of plasma protein-bound ICG and allows uptake of water-soluble sorbitol, the difference E(sorb) - E(ICG) has been suggested as a measure of capillarization. We propose an alternative hypothesis: that the sinusoidal permeability-surface area products for sorbitol and ICG are reduced in proportion by liver disease (proportional reduction hypothesis). Based on the sinusoidal perfusion model, predictions were produced from both hypotheses for the relation between E(sorb) and E(ICG) and the additional effects of capillarization were described. By use of liver vein catheterization, E(sorb) and E(ICG) were simultaneously measured during continuous infusions in 53 human subjects with varying degrees of liver disease. The data were in better agreement with the predictions of the proportional reduction hypothesis than with the shunt hypothesis. Even though both intrahepatic portosystemic shunts and sinusoidal capillarization are known to occur in cirrhosis and also may have influenced our data, they appeared to be of minor importance from a kinetic point of view. These findings favor the proportional reduction hypothesis and do not support the use of systemic nonrenal clearance of sorbitol as a measure of "functional liver blood flow."

Sorbitol removal by the metastatic liver: a predictor of systemic toxicity of intra-arterial chemotherapy in patients with liver metastases

BACKGROUND/AIM

Hepatic arteriovenous shunting in the metastatic liver reduces the advantages of intraarterial infusion of chemotherapeutic agents because of the passage of drugs into the systemic circulation. The aim of this study was to quantitatively assess spontaneous functional hepatic arteriovenous shunting in patients with liver metastases and to determine its implication in the increase in systemic toxic effects of intra-arterial infusion chemotherapy with floxuridine.

METHODS

Twenty-five patients who underwent implantation of arterial ports for regional chemotherapy of liver metastases were studied. Functional hepatic arterio-venous shunting was evaluated through the bioavailability of intra-arterially administered D-sorbitol, a safe, natural compound whose kinetic features make its hepatic clearance flow dependent. In addition, D-sorbitol hepatic clearance (a parameter reflecting functional liver blood flow) and common liver function tests were evaluated for each studied patient. Patients were then grouped with respect to the percentage of medically-assessed liver occupation by metastases and with respect to systemic toxicity of the chemotherapeutic treatment. Both univariate and multivariate analyses by Student's t-test and stepwise logistic regression, respectively, were performed in both groups for each of the evaluated parameters (age, liver function tests, D-sorbitol hepatic clearance and arterial bioavailability).

RESULTS

Arterial bioavailability of D-sorbitol ranged between 0.05 and 0.72 and was significantly greater in patients with more than 50% liver occupation (0.39+/-0.19) compared with those with minor liver involvement (0.17+/-0.13; p = 0.003); it was also significantly greater in patients experiencing high-grade systemic toxicity (0.40+/-0.19) compared with those with low-grade toxicity (0.16+/-0.11; p<0.001). Multivariate analysis showed that arterial bioavailability of D-sorbitol was the only parameter among those evaluated which was able to predict systemic toxicity of this kind of chemotherapy.

CONCLUSIONS

Our results show that, in the metastatic liver, arterial bioavailability of D-sorbitol, an index of functional arteriovenous shunting, varies widely, is significantly greater in patients with massive liver occupation and it is a good predictor of systemic toxicity of intra-arterial regional chemotherapy with floxuridine.

Evaluation of hepatic function in liver cirrhosis: clinical utility of galactose elimination capacity, hepatic clearance of D-sorbitol, and laboratory investigations

Assessment of hepatic function is based on both liver blood tests and functional tests, the extensive application of which is still controversial. The aim of this study was to evaluate the clinical utility of a few selected tests as discriminatory and prognostic indexes: serum albumin, pseudocholinesterase, prothrombin time, as well as galactose elimination capacity and hepatic sorbitol clearance. Two separate studies were performed: Study I to investigate how well these tests assessed severity, and Study II to evaluate their prognostic value. A total of 128 consecutive cirrhotic patients classified according to the Child-Pugh score were included in Study I; Study II was carried out on 47 of these 128 during a two-year follow-up period. Pairwise correlations between all tests and Child-Pugh score yielded higher significant values for liver blood tests than for the functional ones. In Study I functional tests such as galactose elimination capacity and hepatic sorbitol clearance did not appear to be better than conventional biochemical tests in discriminating clinical severity of cirrhotic patients, as defined by Child-Pugh classification. Results of Study II confirmed that in severe liver cirrhosis Child-Pugh score remains the best method for medium- and long-term prognosis and for planning liver transplantation. Functional tests should be reserved for defining the residual functioning liver mass or for studies about functional liver plasma flow.